Medicinal Properties in Whole Foods

Townsend Letter for Doctors and Patients,  August, 2001  by Gina L. Nick

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"Functional foods," "nutraceuticals," "designer foods" and "medicinal foods" are terms that describe foods, and key ingredients isolated from foods, that have non-nutritive or tertiary functional properties. Researchers, healthcare practitioners, laypersons, and the popular media use these words interchangeably. The purpose of this article is to present valid scientific information available on the physiologic actions of known constituents and combinations of constituents, as they naturally occur in "functional foods," highlighting their medicinal and nutritive mechanisms of action in the body.

Chemoprevention and the Crucifers

The scientific community continues to recognize and validate the considerable relationship between vegetable intake and cancer. [1-3] Over 200 epidemiological studies show, with great consistency, that a low consumption of vegetables is directly associated with an increased risk of cancer (Table 1). Epidemiological studies also support the belief that dietary modification, through an increase in vegetable intake, could reduce the risk of cancer by 50% internationally. Specifically, researchers regard cruciferous vegetables, and particularly those that are members of the Brassica plant family, as critical elements in the risk reduction associated with vegetable intake and cancer. [4-8] Further, in people under 55 years of age, cruciferous vegetable intake is inversely correlated with colon cancer incidence and comparatively among smokers the chemoprotective benefits of Brassica consumption are even greater. [9,10] Van Poppel et al. [11] examined 6 cohort studies and 74 case control studies that supported an in verse correlation between Brassica consumption and cancer risk. The association was found to be most consistent for lung, stomach, colon, and rectal cancers, and least consistent for prostatic, endometrial, and ovarian cancers. In studies examining total vegetable consumption an inverse association with cancer risk is also found, with the Brassicas showing the strongest effects as a subgroup.[12] Brassicas also are low in fat, low in calories, and are potent sources of vitamins, minerals, fiber, and phytochemicals, all of which have been linked to cancer prevention. [13-15]

A discussion of the biochemical and physiologic implications of increasing one's intake of cruciferous vegetables will follow. The term "chemoprevention," for the purpose of this research article, refers to the strategic approach of decreasing one's susceptibility to carcinogenic factors through the administration of dietary chemicals, as introduced to the body within the matrix from which they originated (i.e., ingesting the whole vegetable vs. an isolated fraction). The rationale behind emphasizing the use of whole vegetables as opposed to an isolated fraction (considered a chemoprotective agent) is that the degree to which the protective effect of vegetables can be attributed to the nutritional or tertiary components, and to what extent indirect effects such as an equivalent reduction in fat consumption and associated increase in vitamin, fiber and carotenoid intake may be responsible for the protective effect, is not well defined. Nonetheless, the dietary approach of increasing one's intake of cruciferous vegetables to defend oneself from cancer-causing agents has become widely recognized in the medical research community as a realistic and rational practice in the war against cancer. [17]

Medicinal Properties in Whole Foods

Phase II Enzyme Inducers

Exposure to cruciferous vegetables (e.g., kale, Brussels sprouts, Chinese cabbage, bok choy, cabbage, turnips, collards, kohlrabi, rutabaga, cauliflower and broccoli) causes a coordinated metabolic induction of many of the Phase II liver detoxification enzymes that detoxify carcinogenic (cancer-causing) compounds from the body, thus reducing the susceptibility of cells to these substances. Glutathione transferases, NAD(P)H, quinone oxidoreductase, glucuronosyltransferase, and epoxide hydrolase are all Phase II enzymes that inactivate carcinogens.

Mechanisms of action of Phase II enzyme inducers

Phase II enzymes inactivate carcinogens in one of two ways: either through the destruction of the reactive centers of the compounds, or, more often, by conjugation with endogenous ligands, thereby counteracting the toxic properties associated with the carcinogen, and quickening their elimination from the body. Cruciferous vegetables contain water-soluble secondary metabolites referred to as glucosinolate compounds. Interestingly, the medicinal properties of glucosinolates are noted in the writings of Pythagoras and Hippocrates and at least 20 different compounds were identified by the 1980s. [18] All cruciferous vegetables are believed to contain glucosinolates, but Brussels sprouts and broccoli have some of the highest levels.

The glucosinolates found in whole foods are converted by endogenous enzymes into isothiocyanates when they are chewed, crushed in the presence of water, or otherwise injured. This conversion is a natural defense response to predatory and other destructive influences. The tissue damage more specifically results in the release of the endogenous enzyme myrosinase, or thioglucosidase, which cleaves the glucoside bond.